1. Field of the Invention
The present invention relates to a wired circuit board and, more particularly, to a wired circuit board adapted to higher density and higher speed.
2. Description of the Prior Art
A suspension board with circuit mounted on a hard disc drive commonly comprises a metal supporting board, an insulating base layer formed on the metal supporting board, a conductive pattern formed on the insulating base layer, and an insulating cover layer formed on the insulating base layer for covering the conductive pattern. As is known, this suspension board with circuit is configured so that the metal supporting board has an opening formed to correspond to the conductive pattern so as to adjust a characteristic impedance of the conductive pattern and improve a partial flexibility.
It has been proposed in recent years that the suspension board with circuit adapted to higher density and higher speed is designed to have a lower conductor provided under the conductive pattern via the insulating layer in order to reduce a transmission loss of the conductive pattern (Cf. Japanese Unexamined Patent Publication No. 2005-11387, for example).
However, when the known suspension board with circuit having the opening formed in the metal supporting board is provided with such a lower conductor as described in Japanese Unexamined Patent Publication No. 2005-11387 cited above, there may be provided an arrangement as shown in FIG. 8 wherein an edge 28 of the opening 27 formed in the metal supporting board 22 overlaps with a surface of the lower conductor 23 provided under the conductive pattern 25 covered by the insulating cover layer 26 via the insulating base layer 24. In this arrangement in which the edge 28 of the opening 27 overlaps with the surface of the lower conductor 23, adhesion between the metal supporting board 22 and the lower conductor 23 is low at the overlapping portion thereof. Due to this, there is a possible problem that when the suspension board with circuit 21 is bent, the metal supporting board 22 may be stripped from the metal foil 23 at the edge 28 of the opening 27.